Medical diagnostic ultrasound images are formed by generating a high-frequency sound pulse using a transducer, delivering this pulse into the area of interest in the body, receiving the sound echoes from structures within the body, and using information from the echoes to generate an ultrasound image.
Ultrasound imaging involves a transducer that is placed in contact with a patient's skin. An amount of an acoustic coupling medium, such as a conductive gel, is dispensed on the surface of the transducer and onto the patient's skin. The coupling medium couples the transducer with the skin, to assist with transmission of the ultrasonic waves into the body. Ideally the coupling medium provides an acoustic impedance which is part way between that of the transducer and the human body. One commonly used coupling medium is Parker Labs Aquasonic100 transmission gel.
During an ultrasound imaging procedure, insufficient gel, or even a lack of a consistent and desired thickness of the gel, can lead to a reduction in the quality of images produced by the device, and accordingly in measurement values derived from the image.
If, during an ultrasound imaging procedure, no coupling medium were used and the skin was “dry”, then a thin air-gap could, and likely would, exist between the transducer and the skin. In such a case, the resultant large impedance mismatch between the transducer and the air would cause most of the sound energy to be reflected back from the air interface, instead of being transmitted into the medium to be imaged, thus providing a very poor quality and unreliable image. Even in circumstances where a small but insufficient amount of gel was present, whilst an image might be generated, the image quality would again be of poor quality and likely still not permit reliable identification of anatomical features.
In addition to the above, in motor-based ultrasound transducers, “reverberations” may be present due to reflections between the transducer elements and an internal coupling medium (such as an oil). Normally these reverberations only affect very shallow regions. However, they may become prominent in regions with insufficient gel for the same lack-of-coupling reasons described above.
It would be desirable to provide a system and method for indicating, during an ultrasound imaging procedure, whether sufficient gel is present before or during imaging, to determine whether an ultrasound image can be considered reliable, or whether additional gel is required.